Our understanding of human health and the development of new preventive and therapeutic approaches requires the integration in the study of physiology and pathology of the constant exposure of the organism to the microbiota and to evaluate physiology and pathology as states of the whole human metaorganism. In collaboration with geneticists, molecular biologists and bacteriologists, our research is conducted in a multidisciplinary manner combining, cellular immunology, microbiology and genomic approaches. Our work explores the adjuvant role of the microbiota in the induction of protective immunity to pathogens and in the context of vaccine. Over the past fiscal year, our work further explored the role of the microbiota in the control of host immunity at barrier sites including the gut, skin and lung. Current work from our group explores the role of defined commensal species in the regulation of skin and gut immunity. In particular, our research explores the mechanism by which defined commensal species or bacterial products control tissue immune homeostasis and promote adaptive immune responses in the context of steady state, infection and tissue inflammation. Notably our work identified key antigen presenting cells responsible for the mediation of responses to commensals in the context of steady state and inflammation. Our work also uncovered a unique role for commensal specific T cells in the promotion of both tissue immunity and tissue repair. Our work also addresses how a dysregulation in the composition of commensal populations and/or aberrant responses against commensals during infection or inflammation can lead to pathogenic responses.